key_gen

#!/bin/env php

<?php
/**
 * Generate cryptographic keys used in the application.
 *
 * @author Dusan Mitrovic <dusan@dusanmitrovic.xyz>
 * @licence https://opensource.org/licenses/GPL-3.0 GNU General Public License, version 3
 */
define('KEYS_DIRECTORY', __DIR__.'/keys');
define('PRIVATE_KEY_PATH', __DIR__.'/keys/private.pem');
define('PUBLIC_KEY_PATH', __DIR__.'/keys/public.pem');
define('PUBLIC_KEY_CRYPTO_DIGEST_ALGORITHM', 'sha512');
define('PUBLIC_KEY_CRYPTO_KEY_LENGTH', 4096);
define('WRITE_ERROR', 'Unable to write to the disk, check permissions.');

/**
 * Generates a public key cryptography key pair in string representation with the provided options.
 *
 * @return array public/private keypair
 */
function generate_public_key_crypto_key_pair(array $options): array
{
    $key_pair = openssl_pkey_new($options);
    $key_pair_details = openssl_pkey_get_details($key_pair);

    openssl_pkey_export($key_pair, $private_key);

    return [
        $private_key,
        $key_pair_details['key'],
    ];
}

/**
 * Write the file to the disk
 *
 * @param string $path
 * @param mixed $data
 *
 * @throws \Exception
 */
function write_to_file(string $path, $data): void
{
    if (file_put_contents($path, $data) === false) {
        throw new Error(WRITE_ERROR);
    }
}

if (!file_exists(KEYS_DIRECTORY)) {
    if (!mkdir(KEYS_DIRECTORY, 0755)) {
        throw new Error(WRITE_ERROR);
    }
}

if (!file_exists(PRIVATE_KEY_PATH) && !file_exists(PUBLIC_KEY_PATH)) {
    /*
     * Getting the string representation of private and public keys to be stored in a file
     *
     * Supported public key cryptography algorithms include:
     * OPENSSL_KEYTYPE_RSA,
     * OPENSSL_KEYTYPE_DSA,
     * OPENSSL_KEYTYPE_DH,
     * OPENSSL_KEYTYPE_EC
     */
    [$private_key, $public_key] = generate_public_key_crypto_key_pair([
        'digest_alg' => PUBLIC_KEY_CRYPTO_DIGEST_ALGORITHM,
        'private_key_bits' => PUBLIC_KEY_CRYPTO_KEY_LENGTH,
        'private_key_type' => OPENSSL_KEYTYPE_RSA,
    ]);

    write_to_file(PUBLIC_KEY_PATH, $public_key);
    write_to_file(PRIVATE_KEY_PATH, $private_key);

    // The private key must only be accessible by the owner
    if (!chmod(PRIVATE_KEY_PATH, 0600)) {
        throw new Error(WRITE_ERROR);
    }
}